This invention relates to the art of electronically locating or otherwise mapping a touch to an input device. Examples of a touch-responsive input device with which the invention can be used include a touch screen on a video display terminal, a position indicator, a switch panel, and a touch tablet.
More particularly, the invention provides a method and apparatus for locating with an electronic circuit a touch to an unpatterned and selectively electrically conductive layer. The touch location which the invention provides has advantages in terms of accuracy and precision, and repeatability.
Video touch terminals with unpatterned screens are known, as described in U.S. Pat. No. 4,476,463. The unpatterned screen in principle can locate a touch anywhere, not just within the confines of a segmented or otherwise patterned screen.
The touch which can be mapped in the practice of the invention typically is a touch by a human finger. The invention can however be used to locate other touches, such as with an electrically conductive probe and, in another instance, a touch with an electrically active probe that introduces a measuring signal to the electrically conductive layer at the location of the touch. In general, a touch by a finger or passive probe couples an electrical shunt impedance to the selectively conductive layer. Both the location of the touch impedance on the layer, and the value of the impedance, are in general unknown. The location is the quantity which it is desired to measure. The measurement is complicated by the unknown value of the touch impedance. The touch generally presents a complex electrical impedance with an imaginary, capacitive component and with a real, resistive component. The magnitudes of both components can vary from touch to touch, particularly with a human touch, and can vary with environmental conditions such as temperature and humidity. These unknown and varying factors of a touch make it difficult to map the touch readily and accurately with known techniques.
Moreover, as the art of connecting a selectively conductive layer to a source advances, and provides more uniform electrical patterns on the layer, there is an increasing need to measure the effect of the touch impedance, and thereby to locate it, with accuracy, precision and repeatability. The co-pending and commonly assigned application for patent entitled "Method and Apparatus for Improved Touch Mapping Sensitivity", Ser. No. 676,186 filed concurrently herewith, describes such advances in connecting a source to the conductive layer.
Accordingly, an object to this invention is to provide a method and apparatus for electronically mapping a touch to an unpatterned and selectively electrically conductive layer and which are characterized by relatively high accuracy and precision.
Another object of this invention is to provide a method and apparatus for electronically locating a touch to an unpatterned and selectively electrically conductive layer and which provide substantially uniform accuracy and precision in response to a relatively wide variety of touch impedances.
Further objects of the invention are to provide a method and apparatus of the above character which are suitable for commercial implementation at relatively low cost.
Other objects of the invention are set forth hereinafter.